CACalomino
12-19-2005, 11:12 PM
I keep seeing ? here on Socal about what injectors to go with 660s or 720's etc well today I was reading the New Sport Compact Car and a reader wrote in what injectors he should go with for his nissan Se-R build up and how does one determine what they need for there needs. He did not want to small or two big of an injector. So that I dont screw up the info in translation I will just type what was writen in the mag. I found it to be realy helpful and figured it would help somebody here enjoy and read on.
-Chris
Fist off, you need to be sure teh ECU knows what size injectors your have. The ECU just tells the injectors to open for a certain amount of time and assumes the injectors will flow the same amount during that time that they did back when the ECU was programmed. If your change from a 260CC/min injectors to 550 cc/min injectors, the ECu will have to send a shorter pulse to deliver the same fuel.
Once your've handled that task your need to make sure the injector is big enough for your power goals. this is a simple. Just plug your pipe dreams into this formula:Horse Power X B.S.F.C. divided by # of injectors X Duty Cyle = Injector flow (lb/hr)
BSFC just means brake specific fuel consumption, or how much fuel is your engine takes to make power. Most naturally-aspirated engines will consume about 0.5 pounds of fuel per horsepower,per hour, so use 0.5 lb/hp-hr in this formula. If you're turbocharged, try 0.6 or even 0.65. BSFC might be lower if youre funning on the ragged edge of too lean, or if your have really hight octane fuel that lets your advance timing and make more power from the same fuel. None of that matters here, though, since your want a conservative number tat will ensure your injectors aren't too small.
For duty cycle, your want to use 0.80. this means the injectors are open 80% of the time. Not only is this about the highest duty cyle you can run and still have the injectors follow the ECU's commands accurately, but its the duty cycle at witch injectors are flow rated. Your have to use the 0.80 if you want the number from this fromula to mean anything when you go to the injector store.
So if u think you can make 200 crank HP, the formula works out like this 200 X 0.50 devided by 4 X 0.80 = 31.25lb/hr
Which is great, except for the fact that nissan injectors are all rated in CC/min. You now need to plug 31.25 into another formula to convert to metric units
Flow (cc/min) = Flow (lb/hr) X10.5
Wich would give you 328cc/min. Time to shop for something at least that big. Dont forget of course, to use flywheel horespower in that formula. IF u use wheel Horsepower, the result will be too small an injector
-Chris
Fist off, you need to be sure teh ECU knows what size injectors your have. The ECU just tells the injectors to open for a certain amount of time and assumes the injectors will flow the same amount during that time that they did back when the ECU was programmed. If your change from a 260CC/min injectors to 550 cc/min injectors, the ECu will have to send a shorter pulse to deliver the same fuel.
Once your've handled that task your need to make sure the injector is big enough for your power goals. this is a simple. Just plug your pipe dreams into this formula:Horse Power X B.S.F.C. divided by # of injectors X Duty Cyle = Injector flow (lb/hr)
BSFC just means brake specific fuel consumption, or how much fuel is your engine takes to make power. Most naturally-aspirated engines will consume about 0.5 pounds of fuel per horsepower,per hour, so use 0.5 lb/hp-hr in this formula. If you're turbocharged, try 0.6 or even 0.65. BSFC might be lower if youre funning on the ragged edge of too lean, or if your have really hight octane fuel that lets your advance timing and make more power from the same fuel. None of that matters here, though, since your want a conservative number tat will ensure your injectors aren't too small.
For duty cycle, your want to use 0.80. this means the injectors are open 80% of the time. Not only is this about the highest duty cyle you can run and still have the injectors follow the ECU's commands accurately, but its the duty cycle at witch injectors are flow rated. Your have to use the 0.80 if you want the number from this fromula to mean anything when you go to the injector store.
So if u think you can make 200 crank HP, the formula works out like this 200 X 0.50 devided by 4 X 0.80 = 31.25lb/hr
Which is great, except for the fact that nissan injectors are all rated in CC/min. You now need to plug 31.25 into another formula to convert to metric units
Flow (cc/min) = Flow (lb/hr) X10.5
Wich would give you 328cc/min. Time to shop for something at least that big. Dont forget of course, to use flywheel horespower in that formula. IF u use wheel Horsepower, the result will be too small an injector